Natural gas, as it comes from the ground, is not salable because it contains components that make it unsuitable for long distance transportation. For example, produced natural gas is almost always saturated with water vapor that must be removed in order to prevent water from condensing in a long distance pipeline, to prevent the formation of gas hydrates and to avoid expending substantial amounts of energy to transport water. Similarly, it makes perfect sense for an operator to remove any liquefiable hydrocarbons because they usually bring better prices when sold separately as liquids than as gas phase components sold to a gas pipeline.
Contaminants, such as hydrogen sulfide and carbon dioxide, also must be removed because pipeline companies do not want to accept natural gas with greater than a very small percentage of these components. It makes perfect sense to remove hydrogen sulfide because, when burned, it creates sulphur dioxide which easily hydrolyses to produce sulfuric acid which is very corrosive thereby creating problems for the customers of pipelines. In addition, an inappropriate amount of hydrogen sulfide causes steel, such as in pipelines, valves and compressors, to weaken thereby creating a safety hazard. Carbon dioxide is desirably removed because it hydrolyses easily to create carbonic acid, a weak acid that is nevertheless corrosive over ordinary periods of time. In addition, carbon dioxide reduces the heating value of natural gas beyond its simple dilution of natural gas. It will accordingly be apparent that gas pipelines have long required the removal of a variety of contaminants from natural gas offered to them.
It is accordingly not surprising that the industry has developed a rather wide variety of gas treating equipment to remove water, liquefiable hydrocarbons, carbon dioxide, hydrogen sulfide, and other contaminants from natural gas. The standard technique for removing hydrogen sulfide and carbon dioxide is to contact natural gas with an amine to remove the carbon dioxide and/or hydrogen sulfide and regenerate the amine by heating it so the carbon dioxide and/or hydrogen sulfide comes out of solution. It is this technique to which this invention most nearly relates.
Relevant to this invention are the disclosures in U.S. Pat. Nos. 3,758,603; 4,853,012; 5,201,919; 6,063,163; 6,399,030; 6,740,230 and 6,893,484.